Question

1. 
   (a) Figure 2 shows the dependence of the voltage on time during anodizing of aluminium at 5 mA cm2in 0.4 mol dm-3 phosphoric acid at 293 K. Explain the processes that are occurring on the aluminium surface during the anodizing process. 25 15 0 50 100 150 250 300 350 450 time (s) Figure 2: Voltage response during anodizing of aluminunn for 450 s at 5 mA cm-2 in 25 wt% sulphuric acid at 0oC. The voltage after anodizing for 450 s is 17 V
   
2. Sketch a cross-section of the anodic film that is formed. Label the features of the film. Give the size of the features and the thickness of the film.   

• Density of alumina: 2.5 g cm^-3.
• Molar mass of aluminium: 27 g.
• Molar mass of oxygen: 16 g.
• Faradays constant: 96500 C.
• Electric field for ionic migration: 8 x 10⁶ V cm^-1.

Answer 1

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